System for associating inventory with handling equipment in shipping container yard inventory transactions

ABSTRACT

A system is provided to associate containers with handling equipment (HE) in a container storage facility. In the system an operation detector, such as a twistlock sensor that indicates when a container is picked up or dropped off, is installed on a first HE which is a piece of container handling equipment (CHE) that can lift the container. An event detector, such as a vibration sensor or distance measuring radar, is further installed on a second HE that is a tractor with an attached chassis for receiving and transporting a container. The event detector indicates when a container-operation-related event, such as a container pick up or drop off, occurred on the tractor chassis. The two detectors (operation and event) are used by a processor to associate the container with either the CHE or the tractor. The operation and event detectors can further be used in conjunction with position sensors such as a GPS sensor to accurately determine the position of the tractor and the CHE in a container yard. When the position sensors degrade in performance, an additional motion detector such as a speed sensor can be used to determine the tractor&#39;s distance from the CHE to locate an appropriate tractor involved in the operation.

BACKGROUND

1. Technical Field

The present invention relates to an inventory tracking system used in ashipping container storage yard. More particularly, the presentinvention relates to the association of inventory handling equipment(HE) used to move containers in a shipping container storage yard withthe containers moved by the HE as located by the inventory trackingsystem.

2. Related Art

Over the recent decade, the number of shipping containers handled incontainer yards has increased dramatically. To improve the efficiency ofcontainer terminal material handling processes, inventory trackingsystems have been developed to track and monitor what really takes placein the yard. Such an inventory tracking system can employ real-timepositioning technology (such as Global Positioning System (GPS) andReal-time Locating System (RTLS)) and wireless communications to tracklocations of containers by actively tracking the movement and locationsof container handling equipment (HEs) that pick up, move, and set downthe containers. The inventory tracking system then records the trackinginformation to an inventory tracking database and interfaces with aTerminal Operating System (TOS) to update container locations whenever aHE picks up or sets down a container. Such inventory tracking systemsare designed to improve the accuracy of the container yard inventory andthereby reduce lost containers, maximize TOS performance, and improvethe efficiency of HEs.

HEs can be categorized into two broad types: (1) lift equipment—any typeof HE that is capable of lifting a container and setting it down on theground, on top of another container, or onto another HE fortransportation, and (2) transport equipment—any type of HE that iscapable of moving a container from one location to another but is notcapable of lifting the container and setting it down. Typical liftequipment includes top picks (also referred to as top lifts or toploaders), side picks (also referred to as side lifts, side loaders orempty handlers), reach stackers, straddle carriers, rubber tiredgantries (RTGs), rail mounted gantries (RMGs), and quay cranes. Typicaltransport equipment includes over-the-road (OTR) trucks and tractors(also referred to as yard tractor, tug, UTR (Universal Tractor Ross),jockey truck, hustler, yard hustler, etc.). Both OTR trucks and tractorscan have an attached chassis (also referred to as street chassis,trailer, bomb cart, yard chassis, terminal trailer, and so on) which arecapable of carrying one or more containers.

In this description, lift equipment is referred to as container handlingequipment (CHE) and transport equipment is referred to as tractor-typeHE or simply as tractors. And HE is used for both CHE and tractors.

Since inventory tracking systems track the containers by tracking piecesof HE, it is critical to ensure that the association between a containerand the HE that moves it is correct. For example, assume a CHE or a unitof lift equipment picks up a container, Container C1 so labeled forpurposes of discussion, from its location in a shipping yard and puts itonto the chassis of a tractor labeled Tractor1 for this discussion. Thesystem then associates Container C1 with Tractor1 and identifies thelocation of Tractor1 as the location of Container C1 until the nexttransaction on Container C1.

Next consider a situation where the CHE sets down Container C1 onto thechassis of Tractor1, but there happens to be another tractor, Tractor2,right behind Tractor1 waiting for its turn to receive a container.Further assume that due to errors in the positioning sensors andtherefore errors in the position estimates of the two tractors, theposition estimate of Tractor2 appears to be closer to that of the CHEthan the position estimate of Tractor1. The system identifies Tractor2as the tractor that receives Container C1 from the CHE and associatesContainer C1 with Tractor2. As a result, the system assigns the locationof Tractor2 as the location of Container C1, while in reality ContainerC1 is on top of Tractor1. Moreover, the error propagates since such anerroneous association leads to erroneous associations in subsequenttransactions on Container C1. Thus, erroneous tracking and locationinformation has been generated due to incorrect associations betweencontainers and HEs.

To ensure correct association between containers and HEs, the inventorytracking system needs to correctly identify the HEs involved in eachcontainer inventory transaction. Typically, the inventory trackingsystem recognizes a container transaction based on information fromsensors such as the twistlock sensors/switches. Twistlocks aremechanisms installed at the four corners of a CHE's spreader bar tosecure containers in transit on the CHEs. Twistlock systems includeelectronic components (e.g., motors, control circuits, andsensors/switches) to enable remote operation of the mechanicalcomponents. Two types of sensors/switches are typically used tofacilitate the operation of an electronic twistlock. For the convenienceof description, these two types of sensors/switches are referred toherein as twistlock contact sensors and twistlock engagement switches.When a CHE picks up or sets down a container, these twistlocksensors/switches change their outputs or status indication. For example,before a CHE picks up a container, all four twistlocks at the fourcorners of the spreader bar of the CHE must be engaged to secure thecontainer onto the spreader bar for lifting; as the twistlocks areengaged, their corresponding twistlock engagement switches will changetheir status from “disengaged” (or “unlocked”) to “engaged” (or“locked”) to indicate the engagement of the twistlock. Based on thischange, the CHE can detect the occurrence of a container pickupoperation and report to the inventory tracking system its own ID, thepickup operation, and the time the operation occurs. Similarly, when aCHE sets down a container, the twistlocks are disengaged to release thecontainer from the spreader bar, which leads to a change from “engaged”(or “locked”) to “disengaged” (or “unlocked”) in the status of twistlockengagement switches. Thus, the inventory tracking system in this wayobtains information regarding the operation (picking up or dropping off)and the CHE that performs the operation. The correct association betweencontainers and HEs then hinges on the correct recognition of thetractors that receive or provide the containers.

To ensure correct association between containers and HEs, some prior artinventory tracking systems have transponders and readers installed onthe HEs. In one prior art system, transponders are installed on tractorswhile readers are installed on CHEs. Whenever a CHE picks up a containerfrom (or drops off a container onto) the chassis of a tractor, thereaders on the CHE read the transponders on the tractor and identify thetractor based on the information (e.g., tractor ID) from thetransponders. However, such transponder-reader-based mechanisms requireline of sight or close proximity for readers to read transponders.Despite the fact that multiple readers/transponders are typicallyinstalled on each HE to maximize the possibility of line ofsight/proximity (which results in a higher cost), readers often stillfail to detect transponders on tractors. Moreover, thetransponder-reader-based mechanisms are vulnerable to interference andrequire a relatively high level of maintenance.

Other prior art inventory tracking systems install bar codes on tractorsand scanners (or cameras) on CHEs. Similar to transponder-reader-basedmechanisms, the scanners (or cameras) on a CHE read the bar codes on thetractor and the tractor is identified based on the bar codes. Thedrawbacks of such mechanisms include the line-of-sight requirement,performance degradation due to bad weather (especially if cameras areused) as well as damage to or soiling of the bar code (making itunreadable). In addition, the location of the bar codes can also be aproblem. For example, a bar code on the side of a tractor can bedifficult for a crane, which is much taller than a tractor, to read.Also a bar code on top of a tractor is difficult for a top pick, whichis not much higher than a tractor, to read. To solve this problemscanners or cameras can be installed on a top pick's spreader bar, whichcan be much higher than a tractor, but scanners or cameras installed ona spreader bar are prone to damage.

Some other inventory tracking systems simply employ higher-accuracypositioning sensors such as GPS sensors to improve the positioningaccuracy; however, this solution leads to a (significantly) higher cost.Furthermore, the improvement in accuracy is still limited due to theharsh environment for the positioning sensors. For a GPS-basedpositioning system, multipath and long periods of GPS blockage arecommon in a canyon-like environment formed by stacked containerssurrounding the tractors, which limit the achievable accuracy even for ahigher-accuracy GPS (or DGPS).

SUMMARY

In accordance with the embodiments of the present invention, an eventdetection apparatus, adapted for use with transport equipment (i.e.,tractors) is provided for detecting container-operation-related eventsoccurring to tractors in a container yard. In one embodiment, the eventdetection apparatus includes a vibration detector for measuringvibrations of the tractor and a processor for receiving information fromthe vibration detector and detecting container-operation-related eventsoccurring to the tractor.

The container-operation-related events detected by the processor of theevent detection apparatus can include two types of events: a containerpick up from the chassis attached to the tractor and a container dropoff onto the chassis of the tractor. More specifically, thecontainer-operation-related events can include at least one of thefollowing eight types of events: (1) a container drop off in the middleof the chassis attached to the tractor, (2) a container drop off at thefront of the chassis, (3) a container drop off at the rear of thechassis, (4) a container pick up in the middle of the chassis, (5) acontainer pick up at the front of the chassis, (6) a container pick upat the rear of the chassis, (7) chassis engagement (i.e., attachment ofa chassis to the tractor), and (8) chassis disengagement (i.e.,separation of a chassis from the tractor).

In one embodiment, the processor detects the occurrence ofcontainer-operation-related events by collecting vibration measurementsfrom the vibration detector when the vibration measurements arerelatively large (indicating a possible occurrence of acontainer-operation-related event). The processor further maintainsawareness of the loading status of the tractor based on the detection ofcontainer-operation-related events. In a further embodiment, the eventdetection apparatus also includes a speed detector for providinginformation pertaining to whether the tractor is at near-zero speedincluding zero speed. Since container-operation-related events do notoccur unless the tractor is stopped or almost stopped, the eventdetection apparatus only collects vibration measurements when thetractor is at near-zero speed including zero speed.

In one separate embodiment, the event detection apparatus includes acontainer-presence or position detector and a processor. Thecontainer-presence detector detects the presence of at least onecontainer on a chassis of the tractor without determining a distancefrom the tractor cab to the position of the container on the cab.Alternatively, with a position detector such as a radar system, LIDAR orother distance-measuring device, a measurement of the distance betweenthe tractor cab and container can be provided to determine the locationof one or more containers placed on the chassis. The presence detector,such as a camera or a radar device with a short range can stilldetermine a location of the container on the chassis without measuringdistance. The camera can be angled to only detect presence when thechassis is on a front portion, rather than rear portion of the chassis.Similarly, a short-range radar device can determine when a container ison the front of the chassis, but not the rear, and in combination with avibration detector can determine where a container is located on thechassis. The processor receives the status of presence and in some casesthe distance and detects container-operation-related events occurring tothe tractor based on changes in the status of presence as well as thedistances before and after the changes.

A further embodiment of the present invention includes an inventoryassociation method for associating containers with HEs in a containerstorage facility. The inventory association system includes an operationdetector (such as a twistlock sensor that indicates when a container ispicked up or dropped off) installed on a CHE (which can lift andtransport a container), an event detector (such as a vibration detectionsensor) installed on a tractor (which can have a chassis attached to itfor receiving and transporting a container), a communication link, and aprocessor for associating containers with HEs. The operation detectorprovides information indicating an occurrence of a container operationconducted by the CHE, and the container operation includes at least twotypes: a container pickup operation and a container drop off operation.The event detector provides information indicating an occurrence of acontainer-operation-related event occurring to the tractor, and thecontainer-operation-related event includes at least two types: acontainer pick up from the chassis and a container drop off onto thechassis. The communication link connects the operation detector and theevent detector with the processor for transmitting information fromthese two detectors to the processor.

In method steps with the operation detector and event detector, theprocessor detects an occurrence of a container operation as well asrelevant information including an operation type and a time ofoccurrence based on the information from the operation detector. Theprocessor also detects an occurrence of a container-operation-relatedevent as well as relevant information including an event type and a timeof occurrence based on the information from the event detector.Subsequently, the processor determines whether thecontainer-operation-event matches the container operation by comparingthe event type with the operation type and by comparing the time ofoccurrence for the event with the time of occurrence for the operation.If a match is found, the processor further associates the containeroriginally associated with one of the two HEs with the other based on atleast one of the two types: the operation type or the event type.

In another embodiment that relies on CHE position provided either inconjunction with the event detector or separate from it, the inventoryassociation system includes a first mobile unit on a CHE for determiningthe CHE's position and occurrences of container operations performed bythe CHE, a second mobile unit on a tractor for determining the tractor'sposition and motion (e.g., speed). The system further includes aprocessor for associating containers with the HEs, and a communicationlink between the first and second mobile units and the processor toenable information exchange.

In this embodiment, the first mobile unit can include a firstpositioning unit for providing first positions of the CHE and anoperation detector for providing information indicating an occurrence ofa container operation performed by the CHE. The second mobile unit caninclude a second positioning unit for providing second positions of thetractor as well as confidence levels of the second positions and amotion detector for providing information pertaining to motion of thetractor. The first and second positioning units can include devices suchas a GPS sensor, a transponder, or a similar device for identifying HEpositions. The motion detector in the second mobile unit can be a speedsensor or an accelerometer for determining the tractor's motion, whichcan be used to determine a distance from a last trustworthy positionwhen the confidence levels of the second positions are relatively low.The processor of the inventory association system then detects anoccurrence of a container operation based on the information from theoperation detector and determines the location of the containeroperation based on the first positions. The processor further determineswhether the tractor is involved in the container operation based on thelocation of operation, the operation type, the second positions, and thedistance from the last trustworthy position of the tractor. If thetractor is determined to be involved in the container operation, theprocessor further associates the container in the container operationwith either the CHE or the tractor based on the operation type.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIGS. 1A and 1B illustrate a container inventory transaction, where aCHE has just picked up a container from or is about to drop a containeroff onto the chassis of a tractor. Components of a GPS-based inventorytracking system are also shown in the figures.

FIG. 2 shows a first embodiment of an event detection apparatusinstalled on a tractor, which is capable of detectingcontainer-operation-related events occurring to the tractor based on thevibration pattern of the tractor.

FIG. 3 is a flowchart showing the process involved in one embodiment ofthe event detection apparatus for detecting container-operation-relatedevents occurring to the tractor based on the vibration pattern of thetractor.

FIGS. 4A, 4B, and 4C illustrate three container-operation-related eventscorresponding to the following three cases: (1) a 40 ft or 45 ftcontainer has been dropped onto the chassis of a tractor, (2) a 20 ftcontainer has been dropped onto the front portion of the chassis, and(3) a 20 ft container has been dropped onto the rear portion of thechassis.

FIGS. 5A and 5B illustrate the steady-state change in the pitch angle ofa tractor after a container has been put on top of the chassis of thetractor.

FIGS. 6A, 6B, and 6C illustrate another embodiment of an event detectionapparatus installed on a tractor, which detectscontainer-operation-related events occurring to the tractor based on thepresence of a container (or containers) as well as the distance betweenthe container and the tractor.

FIG. 7 shows one embodiment of an inventory association system andmethod for associating containers with HEs.

FIG. 8 is a flowchart showing the process involved in one embodiment ofthe inventory association system and method, in which the association ofcontainers and HEs is based on information from an event detector.

FIGS. 9A and 9B show that errors in position estimates could causeproblems for associating containers with HEs.

FIG. 10 shows another embodiment of the inventory association system andmethod, in which the association of containers and HEs is determined byincorporating the distance of a tractor from its last trustworthyposition (or positions). This distance is referred to as thedistance-to-last-trustworthy-position herein.

FIG. 11 is a high-level block diagram showing a process for associatingcontainers with HEs by incorporating thedistance-to-last-trustworthy-position.

FIG. 12 illustrates the likely positions of a tractor at the time ofoccurrence of a container operation according to another embodiment ofthe inventory association system, which incorporates both thedistance-to-last-trustworthy-position and the profile of a containershipping yard in associating containers with HEs.

DETAILED DESCRIPTION

A. System Overview

FIGS. 1A and 1B provide two views of a container inventory transaction,where a container handling equipment (CHE) 102 has just lifted acontainer 118 from or is going to set down a container 118 onto thechassis 114 (i.e., the terminal trailer or the bomb cart) of a tractor116. Let's assume the CHE 102 (a top pick 102 in this example) has justlifted the container 118. During this container pickup operation, theoperator of the CHE 102 first extends or contracts the spreader bar 120to the appropriate length (10, 20, 30, or 40 feet) based on the lengthof the container 118. The operator then lowers the spreader bar 120 ontothe top of the container 118 so that all of the four twistlocks 124 atthe four corners of the spreader bar 120 are inserted into thecontainer's twist lock receptor holes and the spreader bar 120 is firmlyseated on top of the container. At this point, the twistlock contactsensors that are installed at the four corners of the spreader bardetect the proper seating of the twistlocks and change their outputs(e.g., from “detached” to “contacted”) to indicate that the twistlocksare in place. (No weight is exerted on the twistlock mechanism yet sincethe twistlock has not been engaged but the twistlocks are placed in alocation where engagement of the locks can occur. Based on the contactinformation from the twistlock contact sensors, the CHE operator will beinformed (e.g., via a visual indication such as a lighted bulb lamp orLED) that the twistlocks are in place; the CHE operator can then engagethe electronic twistlocks remotely, typically via a button or switch inthe driver's cab. At this point, the twistlock engagement switches, atype of switch integrated into the electronic twistlock system, changetheir status (e.g., from “unengaged” to “engaged”). After all of thefour twistlocks are successfully engaged (i.e., all of the fourtwistlock engagement switches change their status to “engaged”), theoperator will be informed (e.g., via a visual indication) that it is nowsafe to lift the container. Once the CHE 102 has lifted the containerfrom the chassis 114 of the tractor 116, the container 118 will besuspended by the twistlocks and there will be a small gap between thespreader bar 120 and the top of the container 118; therefore, thetwistlock contact sensors will change their values back to “detached”while the twistlock engagement switches will remain as “engaged”.

When the CHE 102 moves the container 118 to its destination and sets itdown, the spreader bar 120 will once again firmly seat on top of thecontainer 118, which triggers the twistlock contact sensors to changefrom “detached” to “contacted”. Upon receiving this information (e.g.,via visual display), the CHE operator can then disengage the twistlocks,typically via a button or switch in the driver's cab. Subsequently, allof the twistlock engagement switches change their status to“disengaged”; the CHE operator can then lift the spreader bar 120 up torelease the container, which triggers the twistlock contact sensors tochange their status back to “detached”. The CHE operator then moves thespreader bar 120 away, and at this point, the twistlock contact sensorskeep their status as “detached” while the twistlock engagement switchesremain as “disengaged” until the next operation.

FIG. 1A also shows a GPS-based inventory tracking system, in which theCHE is equipped with a GPS receiver 108, a communication unit 106 and aprocessor 104. The CHE 102 is further equipped with twistlock sensors(installed on the spreader bar 120 or embedded in the twistlocks 124)and a height sensor 112. The CHE 102 may also be equipped with aninertial measurement unit (IMU) 110. The processor 104 processes themeasurements from the GPS 108 and the IMU 110 to provide positionestimates of the CHE 102; the processor 104 further communicates theposition estimates as well as other information (e.g., outputs of thetwistlock sensors and the height sensor 112) via the communication unit106 to a central processor (not shown in FIG. 1A), which furtherprocesses and stores the relevant information into an inventory trackingdatabase (also not shown in FIG. 1A). Similarly, as shown in FIG. 1B,the tractor 116 is equipped with a GPS receiver 126, an IMU 132, acommunication unit 134 and a processor 122, and the processor 122provides position estimates of the tractor 116 based on the measurementsfrom the GPS 126 and the IMU 132. The processor 122 furthercommunications the position estimates as well as other information tothe central processor (not shown in FIG. 1B)

Also shown in FIG. 1A, and in more detail in the rotated view of FIG. 1Bare the schematic structure of the tractor 116 with the chassis 114 andthe top pick 102 holding a container 118. The chassis 114 is typicallyattached to the tractor 116 through a fifth wheel coupling mechanism(not shown), which includes a coupling pin (or king pin) on the front ofthe chassis and a horseshoe-shaped coupling device called a fifth wheel128 (shown only in view of FIG. 1B) on the rear of the tractor 116. Thefifth wheel sensor 130 (shown in the view of FIG. 1B) provides thestatus of the fifth wheel coupling (coupled or not) and it may alsoprovide information such as the height of the coupling, the position ofthe king pin, and the status of the lock on the king pin.

Since shipping containers usually are relatively heavy (even when theyare empty), there will be relatively significant impact to a chassis 114when a CHE 102 lifts a container 118 from or sets a container down ontothe chassis 114. Since the chassis 114 is attached to the tractor 116via a fifth wheel coupling, which does little to damp the impact, suchan impact causes the tractor 116 to vibrate (both vertically and in thepitch motion) for a short period of time. Furthermore, the vibrationpatterns depend on the type of the operation (picking up or dropping offa container 118), the weight of the container, and the location of thecontainer on the chassis. For example, the standard chassis is typically40 ft long, which is large enough for one long container (typically 40ft or 45 ft) or two short containers (typically 20 ft in length).Setting down a 20 ft container on the front portion of the chassiscauses a vibration pattern different from that caused by setting down a20 ft container onto the rear portion of the chassis. Hence, thevibration patterns of the tractor 116 can be used to detect theoccurrence of a container-related operation, the type of operation, andwhether the operation is related to a long container, a short containerat the front portion, or a short container at the rear portion of thechassis 114.

B. Event Detection System

1. Event Detection System Based on Vibrations

FIG. 2 shows a first embodiment of an event detection apparatusinstalled on a tractor, which is capable of detectingcontainer-operation-related events occurring to the tractor based on thevibration pattern of the tractor. In this embodiment, the eventdetection apparatus includes a vibration detector 202 for detecting andmeasuring vibrations (which is possibly induced by thecontainer-operation-related events) and a processor 204 for receivinginformation from the vibration detector 202 and for determining theoccurrence of events. The operation-related events can include at leasttwo types of events such as a container pick up from the chassis and acontainer drop off onto the chassis. More specifically, thecontainer-operation-related events can include the following six types:(1) a container drop off in the middle of the chassis, (2) a (short)container drop off at the front of the chassis, (3) a (short) containerdrop off at the rear of the chassis, (4) a container pick up in themiddle of the chassis, (5) a (short) container pick up at the front ofthe chassis, and (6) a (short) container pick up at the rear of thechassis. In another embodiment, the event types can further includechassis engagement and chassis disengagement, which indicate that achassis is being attached to or separated from the tractor,respectively.

The vibration detector 202 for detecting and measuring vibrations of thetractor can be a sound detector that detects sounds caused by the impactof a container operation, an accelerometer that detects the verticalmotion of the tractor, a height sensor that detects the vertical motionof the tractor by measuring the height from the mounting location to theground, an angular motion sensor that detects the pitch motion of thetractor, or an IMU that includes an accelerometer and/or an angularmotion sensor. The processor 204 on the tractor then determines whethera container-operation-related event has occurred based on the (verticalor angular) vibrations measured by the vibration detector 202.

FIG. 3 is a flowchart showing a process employed by the processor 204 onthe tractor to detect an occurrence of a container-operation-relatedevent. The process starts by reading the vibration measurement from thevibration detector 202 at step 302 and determining whether the processis in a recording mode at step 304.

Since vibrations caused by an impact due to a container operationusually last for a short period of time, it can be desirable to collectthe vibration measurements in the whole period for analysis.Alternatively, real-time processing of the vibration measurements can bedesigned to process each vibration measurement in each processing cyclewithout recording the vibration measurements. In the process shown inFIG. 3, the vibration measurements are recorded and then processed. Arecording mode is devised for this purpose and a Boolean variable, e.g.,recording mode, is used to indicate whether the recording mode is activeor not. This Boolean variable is initialized to be 0 (meaning not in arecording mode) when the system first starts.

Referring to step 304, if the Boolean variable is 0 (e.g.,recording_mode=0), the process is not in a recording mode and theprocessor will then proceed to step 306, in which the process determineswhether a recording mode should be started based on the magnitude of thecurrent vibration measurement. If the current vibration measurement isrelatively small (e.g., smaller than threshold_start, a pre-setthreshold selected based on the minimum impact of container operations),no events are determined to have occurred and the process ends and waitsfor the next processing cycle to start from step 302 again. Theprocessing cycle is set to occur at a frequency to assure detection of avibration. The processing cycle can be set the same as (or longer than)the rate of the measurements from the vibration detector. For example,if the rate of the measurements is 0.1 s, the processor executes theprocess as shown in FIG. 3 every 0.1 s or a little longer.

If the current vibration measurement is relatively large (e.g., largerthan the pre-set threshold), indicating a likelihood of acontainer-operation-related event, the process determines that arecording mode should be started and proceeds to step 308 to set theBoolean variable to 1 (e.g., to set recording_mode=1). The process thenstores the current vibration measurement together with other informationincluding the current speed measurement and the current time at step310. Subsequently, the process ends its current cycle and waits till thenext processing cycle to start again at step 302.

If at step 304, the process recognizes that it is in a recording mode(e.g., based on recording_mode=1), the process stores the currentvibration measurement together with other information including thecurrent speed (if available) and the current time at step 312. Theprocess further determines whether the vibration has settled and therecording mode should be ended at step 314. In one embodiment, thedetermination is based on the vibration measurements during apre-defined duration, e.g., between time (t−T) to time t, where time tis the current time and T is the pre-defined duration. That is, if allof the vibration measurements collected between time t−T and time t areall smaller than a pre-defined threshold (e.g., threshold end), theprocess considers the vibration has settled down and proceeds to step320 to end the recording mode by resetting the Boolean variable to 0(i.e., recording_mode=0). If the vibration has not settled, the processwill not end the recording mode and simply exits to wait for the nextprocessing cycle to start at step 302 again.

Once the vibration has settled (as determined at step 314) and therecoding mode has been reset (at step 316), the process then determineswhether a container-operation-related event has occurred based on thecollected vibration measurements at step 318. Further details of thedetermination will be described later with FIG. 4. If an event isdetected at step 318, the process continues to step 322 through step 320to report the event together with other relevant information includingthe type of the event and the time the event occurred. In oneembodiment, the process creates an event table to record suchinformation, and at step 322, the process will then add a line entry tothe event table to record the newly detected event. If the processdetermines that the vibration is not caused by a container operation, itcontinues to step 324 to discard the collected measurement and thenexits to wait for the next processing cycle.

Referring back to step 318, where the process determines whether acontainer-operation-related event has occurred. In one embodiment, thereare at least six types of events. FIGS. 4A-4C illustrate the first threein these six types: (1) a container drop off in the middle of thechassis (FIG. 4A), (2) a (short) container drop off at the front of thechassis (FIG. 4B), (3) a (short) container drop off at the rear of thechassis (FIG. 4C), (4) a container pick up in the middle of the chassis,(5) a (short) container pick up at the front of the chassis, and (6) a(short) container pick up at the rear of the chassis. In anotherembodiment, the event types can further include chassis engagement andchassis disengagement.

Events of different event types cause a tractor to vibrate differently,resulting in different vibration patterns that can be used to determinenot only the occurrence of an event but also the type of the event. Dueto the fact that a picking up operation and a dropping off operation gothrough different operation processes, the vibrations induced by apicking up operation are distinctively different from those induced by adropping off operation. More specifically, a picking up operationrequires the CHE to first land the spreader bar on the container, thenengage the twistlocks, and finally lift the container up, while adropping off operation requires the CHE to first set the container downonto the chassis, disengage the twistlocks, and then pull the spreaderbar up and away. As a result, the difference in the action sequencecreates different signatures in the vibration patterns. Furthermore, themagnitude, frequency, and damping of the vibrations depend on the weightand size of the container and the location of the container (i.e., themiddle, the front, or the rear of the chassis). Thus, by examining thesignatures in the sequence, magnitude, frequency, damping factor, andduration of a vibration pattern (which is collected during a recordingmode), the processor 202 on the tractor can detect whether an event hasoccurred and determine which of the six events occurred.

In one embodiment, the event detection at step 318 employs patternrecognition techniques via a two-stage process. At the first stage, thevibration measurements collected during one recording mode are processedto extract signatures (or features) that are representative of thevibrations. Both time-domain and frequency-domain analysis can beapplied, which include but are not limited to the following: model-basedtime-series analysis, principal components analysis (PCA), singularspectrum analysis, continuous wavelet transform, Fractional Fouriertransform and linear and nonlinear statistical regression techniques.

At the second stage, the extracted features are input to a pre-designedclassifier (or a set of classifiers), which classify the vibrationpattern (as represented by the extracted features) into one of eightclasses, including six classes corresponding to the six types of events,a seventh class representing that no event has occurred, and an eighthclass representing a “can't decide” decision. In another embodiment, theclassifier can classify the vibration pattern into one of ten classes,including the eight classes mentioned above and two classes for the twoevent types: chassis engagement and chassis disengagement. In analternative embodiment, instead of classifying the vibration patterninto a definitive class, the classifier determines a likelihood vectorwhich includes the likelihood that the vibration pattern belongs to eachof the classes. In yet another embodiment, the “can't decide” class canbe discarded and only the remaining seven classes are used. The designof the classifier is based on vibration data collected in experimentswhere the associated events are known. Various classification techniquescan be used for the classifier design, such as fuzzy logic, clustering,neural networks (NN), self-organizing maps (SOM) and simplethreshold-base logic. These techniques and the processes for classifierdesign are well-known to those skilled in the art and are therefore notincluded in this description.

In another embodiment, the event detection at step 318 can use a dynamicmodel to represent vibrations associated withcontainer-operation-related events. In one non-limiting example, themodel is of the form: y(t−t_(event))=f(F_(impact), L_(impact),t−t_(event), n_(noise)), where y is the vibration signal that ismeasured, t is the current time, t_(event) is the time the event firststarts (i.e., the time of the recording mode starts), F_(impact) is theimpact force due to the container operation (or chassisengagement/disengagement), L_(impact) is the (equivalent) location ofthe impact force, and n_(noise) represents the measurement noises. Thedesign of such a dynamic model involves developing a model structurebased on physics of the tractor-chassis system and identifying modelparameters based on data collected in experiments where the event typesare known. Since the design process for dynamic models is well-known tothose skilled in the art, it is not described in detail herein.

With the pre-determined model, the event detection at step 318 then fitsthe vibration measurements into the model to identify F_(impact) andL_(impact) by solving the following equation:

${\begin{bmatrix}{y_{m}\left( {t_{1} - t_{event}} \right)} \\{y_{m}\left( {t_{2} - t_{event}} \right)} \\\vdots \\{y_{m}\left( {t_{n} - t_{event}} \right)}\end{bmatrix} = \begin{bmatrix}{{f\left( {F_{impact},L_{{impact},},{t_{1} - t_{event}},w_{noise}} \right)},} \\{{f\left( {F_{impact},L_{{impact},},{t_{2} - t_{event}},w_{noise}} \right)},} \\\vdots \\{{f\left( {F_{impact},L_{impact},{t_{n} - t_{event}},w_{noise}} \right)},}\end{bmatrix}},$

-   -   where y_(m)(t_(i)−t_(event)) is the vibration measurement at        time t_(i). Subsequently, the event detection at step 318        determines that a container-operation-related event has occurred        if the impact force F_(impact) is larger than a pre-determined        threshold, and the event type is further determined based on the        sign of F_(impact) and the location of the impact, L_(impact)        For example, if the impact force F_(impact) is in the direction        of gravity and the location of the impact L_(impact) is        approximately the center of the chassis, the event type is        determined as “a container drop off onto the middle of the        chassis”.

Variations to the dynamic model as well as the event detection based onthe dynamic model can be determined by those skilled in the art. Forexample, multiple dynamic models can be built, one for each of severalevent types, and the event detection step 318 can fit the vibrationmeasurements into each of the dynamic models and compare the residualerrors. The model that renders the smallest residue error is identifiedas the model representative of the detected vibrations. In sum, if theimpact force F_(impact) corresponding to this model is relatively large(i.e., larger than a pre-determined threshold), acontainer-operation-related event is detected in step 318 and the eventtype is determined as a type corresponding to this particular model. Inaddition to pattern recognition and model matching techniques, othermethods such as information-based algorithm, cognitive-based algorithm,and rule based logics can be utilized to analyze the vibrations and todetect container-operation-related events.

In one embodiment, the event detection and event type determination ofstep 318 can also involve confirming the event detection by checkingwith previous event histories stored in an event table. For example, inaddition to the event information, the event table can further includethe load status of the tractor, including no container onboard, onecontainer in the middle, one container at the front, one container atthe back, two containers (one at the front and the other at the back),etc. If the current event is detected as a container drop off in themiddle of the chassis (e.g., based on the two-stage processing describedabove), the process then checks the status of the tractor as recorded inthe event table, which is the status right before the current event. Ifthe status is empty, the event detection is further confirmed and theprocess can add the current event to the event table and update thetractor status to “one container in the middle”. On the other hand, ifthe status of the tractor in the event table is “one container at thefront”, the current event, which is detected as a container drop off inthe middle of the chassis, could not have happened. Such a conflictindicates either the previous event or the current event has beendetected wrong. The process can then compare the vibration patternscorresponding to these two events and re-assess their types. If theprocess fails to reconcile the detection decision, it may mark bothevents as “can't decide” or add a conflict flag to both of them, or itmay request inputs from the tractor operator or other observingindividual to specify the event types so as to resolve the conflict.

In a further embodiment, the event detection apparatus shown in FIG. 2can also include a speed detector for providing information pertainingto whether the tractor is at near-zero speed including zero speed. Sincethe container-operation-related events typically only occur when thetractor is stopped or almost stopped, the processor 204 can then collectvibration measurements for event detection when the speed detectorindicates that the tractor is at near-zero speed including zero speed.By doing so, vibrations occurring when the tractor is moving, e.g.,vibrations caused by the movement of the tractor and the roaddisturbances, are excluded, thereby reducing the workload of theprocessor 204 and further enhancing the event detection accuracy.

The speed detector can be a speed sensor that directly measures thetractor's speed and the processor 204 determines that the tractor isstopped or almost stopped if the speed measurement is at or near zero(i.e., smaller than a threshold such as 0.1 m/s). Alternatively, anaverage speed can be calculated based on the speed measurements within apre-defined time period (e.g., [t−t_(w), t] where t is the current timeand t_(w) is the duration of the time period) and the processorconcludes that the tractor is stopped or almost stopped if this averagespeed is at or near zero. Alternatively, the speed detector canindicates gear position and the process determines the tractor isstopped if the gear position is put as parked. The speed detector canalso be an accelerometer installed on the tractor. Since the movement ofthe tractor induces relatively small (compared to the impact ofcontainer operations) but persistent vibrations, the measurements of theaccelerometer allows a determination of whether the tractor is stoppedor at near-zero speed. Alternatively, an IMU can be used in place of theaccelerometer.

2. Event Detection Based on Changes in Pitch Angle

FIGS. 5A and 5B illustrate use of a pitch rate sensor that can be usedas the vibration detector to detect vibrations in the pitch motion ofthe tractor as well as a change in the pitch angle before and after thevibrations. The pitch rate sensor can be used either alone, or inconjunction with a device that measures vibrations as described withrespect to FIG. 3. With a pitch rate sensor, the processor 206 on thetractor follows the same process flow as shown in FIG. 3. However, theevent detection and event type determination at step 318 are based onthe steady-state change in the pitch angle of the tractor instead of (orin addition to) the vibration patterns. FIGS. 5A and 5B together showthe steady-state change in pitch angle after a container has been put ontop of the chassis of the tractor. FIG. 5A shows the tractor with anun-loaded chassis attached to it and FIG. 5B shows the tractor with acontainer sitting in the middle of the chassis. Due to the weight of thecontainer, the pitch angle of the tractor increases after a containerhas been put on top of the chassis of the tractor (FIG. 5B) Therefore, apositive change in the pitch angle after the vibrations have settledindicates a container drop off operation while a negative changeindicates a container pickup operation. Thus, at step 318, the processintegrates the pitch angle collected during a recording mode. If themagnitude of the change in angle is relatively large (e.g., larger thana pre-determined threshold corresponding to the minimum change acontainer operation could induce), a container-operation-related eventhas been detected. The operation is a container drop off operation ifthe angle change is positive or a container pick up operation if theangle change is negative.

Since the magnitude of the pitch angle change relates to the momentcreated by the container, which is a combined effect of the weight ofthe container and the location of the container (i.e., in the middle, atthe front, or at the rear of the chassis), additional information isneeded if it is desired to further identify the location of thecontainer. In one embodiment, the maximum value of the vibrationtogether with the duration of the vibration (which indicates thefrequency and damping of the vibrations) are used to determine thelocation of the container on the chassis. In another embodiment, twoclassifiers are designed, one for the container pick up operation andthe other for the container drop off operation; each of these twoclassifiers further classifies the operation into three classescorresponding to the three possible locations of the container on thechassis.

3. Event Detection Based on Container Position Detection

FIGS. 6A-6C illustrate another embodiment of an event detectionapparatus installed on a tractor 116 to detect presence of a containeron the chassis as well as container position by providing a measurementof the distance between the container 118 (or short containers 608, 610)and the tractor 116. In this embodiment, the event detection apparatusincludes a container-position detector 602 for detecting the presence ofa container 118 (or containers 608, 610) on the chassis attached to atractor and for providing a status of presence as well as a distancebetween the container 118 (or containers 608, 610) and the location ofthis container-position detector on the tractor, and a processor 604 fordetecting container-operation-related events occurring to the tractorbased on changes in the status of presence and the distances before andafter the changes. The container-position detector 602 can be installedon the tractor 116, facing backwards above the chassis 118; examples ofthis container-position detector 602 include a radar system, a LIDAR(Light Detection and Ranging), an ultrasonic sensor, and a camera. Asillustrated in FIGS. 6A-6C, if there is a container 118 (or there aretwo containers 608, 610) on top of the chassis, the container-presencedetection means detects the container 118 (or the container 610 at thefront of the chassis) as a target and provides its distance to thecontainer-presence detector 602 (e.g., at the rear of the tractor 116).Techniques for identifying targets and their locations in radar, LIDAR,and ultrasonic images, as well as image processing techniques used toprocess camera images for similar purposes are well-known to thoseskilled in the art; therefore, they are not included in thisdescription.

Since a short container 610 at the front of the chassis 118 can preventthe container-position detector from detecting the presence of a shortcontainer 608 at the rear, it can be necessary to require a CHE operatorto always put a short (e.g., 20 ft) container at the rear of the chassisbefore putting a container at the front and to always pick up thecontainer at the front of the chassis before picking up the container atthe rear. By enforcing such a protocol, the processor unit 604 iscapable of detecting all of the six container pickup and drop off eventsreferenced earlier based on the change in the output (i.e., status ofpresence) of the container-position detector 602. For example, if thestatus of presence changes from “no target” to “target” and the distanceis small (e.g., smaller than a quarter of the chassis length), a regular(40 ft or 45 ft) container has been dropped off in the middle of thechassis. If the status of presence changes from “no target” to “target”and the distance is relatively large, a short container has been droppedoff at the rear of the chassis; if the status of presence remains as“target” but the distance changes from a relatively large distance to asmall distance, a short container has been dropped off at the front ofthe chassis and there are two short containers on top of the chassis.Similarly, the three events corresponding to container pickup operationscan be detected.

4. Event Detection with Container Presence Detection

The event detection apparatus as described with FIGS. 2, 5, and 6 caninclude one or more of many different types of container-presencedetectors to improve the accuracy in determining whether the containerinvolved in the event is at the front or the rear of the chassis. Afirst type of container-presence detector, termed a position detector,includes a radar or LIDAR that can measure a distance from a tractor cabto a container placed on a chassis to determine both its presence anddistance to cab. A second type of container-presence detector can have ashort detection range and its scanning or detection angle can be smallto detect a container presence even if it does not have the capabilityof measuring the distance from a container to the tractor cab. Examplesof such a container-presence detector include short-range ultrasonicsensors, radar, and LIDAR as well as low-resolution cameras. Thiscontainer-presence detector (or non-position detector) can detect thepresence of a container when it is within a certain distance (e.g., onethird of the chassis length) to the detector. That is, thecontainer-presence detector can detect a regular container on thechassis (such as the container 118) and a short container at the frontof the chassis (such as the short container 610), but it may not detecta short container at the rear of the chassis (such as the shortcontainer 608). Alternatively, the container-presence detector can alsobe a motion detector that detects the movement of a container (during apickup or drop-off event) within a pre-determined range (e.g., one thirdof the chassis length).

Even with a long detection range and a relatively large scan angle, acontainer-presence detector by itself may not be adequate in detectingcontainer-operation-related events that involve a container at the rearof the chassis, especially when there is a container at the front of thechassis blocking its view. However, if a container-operation-relatedevent has already been detected, the container-presence detector can beeffective and reliable in supporting the determination of whether acontainer in the middle, at the front, or at the rear is involved.

Accordingly, for an event detection apparatus with a container-presencedetector, the event detection apparatus can first detect acontainer-operation-related event and determine whether it is a pickupor drop-off event based on detectors such as a vibration detector or acontainer-position detector. If the container-presence detector detectsno container, the container involved in the event should be at the rearof the chassis; if the container-presence detector detects a container,the event involves either a regular container in the middle or a shortcontainer at the front. The event detection apparatus can furtherdistinguish these two types based on the load status or the eventhistory of the tractor. For example, if current event is determined tobe a drop off event and the previous event was a container drop off atthe rear of the chassis, the current event must be a drop off of a shortcontainer at the front of the chassis instead of a regular container inthe middle of the chassis.

The container-presence detector can be incorporated into an inventoryassociation system to help determine whether the container operation isrelated to a regular container in the middle of the chassis, a shortcontainer at the front, or a short container at the rear. Such inventoryassociation systems can be based on transponders/readers, positioningsystems, and other techniques that can be used to make inventoryassociations. One embodiment of a method for determining the location ofa container operation with respect to a chassis includes the followingsteps. First, the inventory association system detects a containeroperation performed by a CHE and identifies a tractor as the tractorthat provides or receives the container involved in the containeroperation. The inventory association system then determines the locationof the container on the chassis based on a status of presence providedby the container-presence detector installed on the tractor. That is, ifthe container-presence detector detects a container, the container isdetermined to be at the front or in the middle of the chassis;otherwise, the container is determined to be at the rear of the chassis.For an embodiment of the container-presence detector that cannotdetermine distance, the container-presence detector can have a shortrange that only allows it to detect a container at the front or in themiddle of the container. As will be appreciated by those skilled in theart, a container-position detector, which provides both a status ofpresence and a distance between the container and the tractor, can alsobe used to determine the location of the container operation withrespect to the chassis.

C. Inventory Association System Based on Operation and Event Detection

FIG. 7 shows one embodiment of an inventory association system andmethod for associating containers with HEs that provide for inventoryingcontainers based on detection of two items occurring on a singlecontainer: an operation and an event. First regarding the operationitem, in a container shipping yard, there are a number of CHEs andtractors; FIG. 7 shows one CHE 102 and one tractor 116 for illustrationpurposes. In this embodiment, an operation detector 702 is installed onthe CHE 102, providing information indicating an occurrence of acontainer operation conducted by the CHE. The container operationincludes at least two types: a container pickup operation and acontainer drop off operation. Next for the event, an event detector 704is installed on the tractor 116 (i.e., HE that can have a chassisattached to it for receiving and transporting a container), providinginformation indicating an occurrence of a container-operation-relatedevent on the tractor 116. The container-operation-related event includesat least two types: a container pick up from the chassis 116 and acontainer drop off onto the tractor chassis 116. A processor 706associates containers with HEs based on the information from theoperation detector 702 and the information from the event detector 704.A communication link 708 on the processor 706 links the operationdetector 702 and the event detector 704 with the processor fortransmitting information to the processor.

In another embodiment (not shown), the processor 706 is separated intomultiple local processors with each local processor located on each HEand a separately located central processor. The embodiment shown in FIG.7 with an integrated processor will be described in detail subsequently;however, one skilled in the art can easily recognize that thedescription can easily be applied to have separated processors.

The operation detector 702 on a CHE 102 that is capable of lifting acontainer serves a function different from the event detector 704 on atractor 116 that are capable of receiving and moving the containers. Theoperation detector 702 on a CHE 102 detects container pickup and dropoff operations carried out by the CHE 102 while the event detector 704on the tractor 116 detects container-operation-related events occurringto the tractor.

1.1 Operation Detection Based on Twist-Lock Sensor Indication

The operation detector 704 on a CHE 102 includes a plurality of sensorswitches for providing a status of engagement indicating engagement anddisengagement of mechanisms that secure a container to and release acontainer from the CHE 102. In one embodiment, the operation detectionmeans includes twistlock sensors, such as twistlock contact sensors andtwistlock engagement switches. The processor for the CHE 102 detects acontainer pickup or drop off operation based on the sequence of changesin its twistlock sensors. For example, during a container pickupoperation, the twistlock sensors typically go through the followingthree-step sequence of changes: (1) the twistlock contact sensors changefrom “detached” to “contacted” (indicating the spreader bar of the CHEhas securely contacted on the container), (2) the twistlock engagementswitches change from “disengaged” to “engaged” (indicating the twistlockis in place and engaged (i.e., locked)), and finally (3) the twistlockcontact sensors change from “contacted” back to “detached” (indicatingthe container has been lifted up and the spreader bar is no longerresting firmly on the container and the container is being supported bythe twistlocks of the spreader bar). Similarly, when the CHE 102 setsdown a container, the twistlock sensors go through a similar sequence ofchanges except in the second step the twistlock engagement switcheschange from “engaged” to “disengaged”. There are situations where theCHE 102 operator may engage and disengage the twistlock several times toensure a secure engagement or disengagement, which results in moresteps.

The operation detector 702 includes the twistlock engagement sensor; bymonitoring the changes in the status of the twistlock engagementswitches, the processor for CHE 102 can determine the type of operation;that is, it is a pickup operation if the final status is “engaged” and adrop off operation if the final status is “disengaged”. In anotherembodiment, the operation detector 702 comprises both the twistlockengagement switches and the twistlock contact sensor, and the time atwhich the twistlock contact sensors change from “contacted” to“detached” after the final change in the twistlock engagement switchesis the time when the pickup or drop off operation actually occurs.

1.2 Operation Detection Based on Vibration Detector

Alternatively, the operation detector 702 can include a vibrationdetector similar to that in an event detection apparatus which isdisclosed earlier. The vibration detector provides measurements ofvibrations of CHE 102, which can be used by the processor for CHE 102 todetect an occurrence of a container operation. As will be appreciated bythose skilled in the art, the operation detection based on vibrations ofCHE 102 is similar to the event detection based on vibrations of atractor.

Thus, based on the operation detector, the processor for CHE 102 detectsa container pickup or drop off operation as well as the time theoperation occurs. If a positioning sensor such as GPS or a transponderis available on the CHE, the processor for CHE 102 further determinesthe location of the operation based on the position of CHE 102 providedby the positioning sensor. The processor 706 then communicates thedetection of the operation, including the type (pick up or drop off),the time, and the location, as well as the ID of the CHE to theprocessor 706.

2. Event Detection Based on Event Detector

The event detector on the tractor 116 (or other HEs that are capable ofreceiving and moving the containers) can include a vibration detectorfor detecting vibration patterns induced by thecontainer-operation-related events. The processor for the tractor 116follows the process described in FIG. 3 to detectcontainer-operation-related events as well as the time and the type ofthe events. Alternatively, the event detector can include acontainer-position detector for detecting the presence of a container(or containers) on the chassis attached to the tractor 116 and forproviding a status of presence as well as a distance between thecontainer (or containers) and the location of this container-positiondetector on the tractor. The processor for the tractor detectscontainer-operation-related events occurring to the tractor based onchanges in the status of presence and the distances before and after thechanges. Subsequently, the processor on the tractor communicates to thecentral processor 706 the event information, including the time, theevent type, the location and the ID of the tractor 116.

3. Method Steps for Inventory Association Using Mutual Operation-EventDetection

If an event (i.e., container-operation-related event) is detected, acontainer has been handed over from one HE to another. An event can alsobe detected if a container has been “picked up” or “dropped off” by atractor through chassis engagement or disengagement indicating acontainer has been handed over from one HE to another or it has beenpicked up from or dropped off onto the ground or the top of anothercontainer. As a result, the association between the container and the HEchanges in every operation or event. Therefore, whenever an operation isdetected by a CHE or an event is detected by a tractor, the inventorytracking system needs to update the corresponding container-HEassociation. In one embodiment, upon receiving the detection of anoperation from a CHE or the detection of an event from a tractor, thecentral processor 706 establishes or updates the association byfollowing an association process shown in FIG. 8.

In FIG. 8, the association process starts at step 802, where the centralprocessor checks whether a new operation or event has been reported by aCHE or a tractor. If no new operation or event is reported, theassociation process ends and waits for the next processing cycle tostart at step 802 again. If yes, the association process proceeds tostep 804 to examine whether the reporting is an operation performed by aCHE or an event occurred to a tractor. In one embodiment, theassociation process makes the decision based on the equipment ID in theoperation or event data; if the equipment ID is an ID of a CHE, theassociation process concludes it is an operation reported by a CHE andproceeds to step 806; otherwise, the association process concludes it isan event reported by a tractor and proceeds to step 818. In anotherembodiment, CHEs and tractors add an additional flag in their operationor event reporting, which indicates whether the reported data is anoperation or an event. The association process therefore makes thedecision at step 804 based on that flag.

Since a CHE only detects the occurrence of a container pickup or dropoff operation, it does not distinguish whether it picks up a containerfrom (or sets down a container onto) the ground or the chassis of atractor. Therefore, at step 806, the association process determineswhether the operation is a transaction involving another HE (i.e.,tractor) or not. In one embodiment, the CHE is also equipped with aheight sensor measuring the height of the container and the heightmeasurement at the time the twistlock engagement switches change theiroutput. For example, when a CHE picks up a container from the ground orfrom a container stack, the measurement of the height sensor at the timethe twistlock is engaged has only one of several specific valuescorresponding to the height of one container (if the container is on theground), two containers (if there is one container beneath the containerbeing picked up), three containers (if there are two containers beneaththe container being picked up), and so on. If on the other hand, thecontainer is being pickup from the chassis of a tractor, the measurementof the height sensor when the twistlock is engaged has a valuecorresponding to the height of a container and the height of a chassis.Thus, based on the height included in the location information, anassociation processor can determine whether another HE (i.e., tractor)is involved in the transaction (i.e., the operation is from (or to) thechassis of a tractor). If yes, the process proceeds from step 806 tosteps 818 through 830 to find the correct tractor for association; ifno, the transaction does not involve a tractor and the process continuesfrom step 806 to step 808 to determine whether the operation is a pickupor a drop off. Alternatively, if the height information is notavailable, the processor always assumes a tractor is involved in theoperation and proceeds to step 818 through 830.

At step 808, the association process examines the type of the operationincluded in the operation reporting. If the operation is a containerdrop off, the process then removes the association between the CHE andthe container at step 810. In one embodiment, the association processmaintains an association table in which there is an entry for each HEthat is currently operating in the shipping container yard, and eachentry contains at least the ID of the HE and the ID of the container theHE is currently associated with. For example, if a CHE A has picked upcontainer C1 and is moving it, the entry for CHE A is [A, C1, t1], wheret1 is the time the association is established. When CHE A sets downContainer C1 on the ground, the association process removes theassociation between CHE A and Container C1 by changing the entry for CHEA to [A, null, t2], where t2 is the time the association is removed. Atstep 816, the association process then reports the location of thecontainer to the inventory tracking database for update.

If a container pickup operation has occurred, the association processidentifies the pickup operation at step 808 (based on the reportedoperation type) and creates an ID for the container at step 812. Theassociation process then associates the container with the CHE at step814. In one embodiment, this is achieved by changing the entrycorresponding to the CHE to [CHE ID, container ID, current time] in theassociation table. If the inventory association system furtherinterfaces with an inventory tracking system, the processor can inquirethe inventory tracking system with the ID of the CHE and the time ofoccurrence of the operation for the location of the CHE (as the locationof the operation) as well as the ID of the container at the location.Then at step 816, the association process updates the inventory trackingdatabase to show the container has been picked up by the CHE and toremove or expire the data record that shows the container at itsprevious specified location.

In the embodiment shown in FIG. 8, the event type does not includechassis engagement and disengagement; therefore, an event will alwaysinvolves a CHE and a tractor. Thus, if an event has been reported (asdetermined at step 804), the association process continues to steps 818through 830 for association. Similarly if the operation in step 806 doesinvolve a tractor the process continues with steps 818 through 830. Thefollowing description assumes an event has been reported; however, theprocessing for cases where the reported operation involves a tractor issimilar. As described before, an event is essentially an operation fromthe tractor's view point. In one embodiment, the tractor detects sixtypes of events, which have been described earlier with respect to FIG.2. For the completeness of the description, these six types are repeatedhere as follows: (1) a container drop off in the middle of the chassis(FIG. 4A), (2) a (short) container drop off at the front of the chassis(FIG. 4B), (3) a (short) container drop off at the rear of the chassis(FIG. 4C), (4) a container pick up in the middle of the chassis, (5) a(short) container pick up at the front of the chassis, and (6) a (short)container pick up at the rear of the chassis.

Since events are caused by operations, the association process searchesa transaction table for candidate operations at step 818 when the newevent is reported. The transaction table is created and maintained bythe association process to keep a record of all the containertransactions between HEs. Each entry in the transaction table containsat least the following information: the ID of the HE that provides thecontainer, the ID of the container, the ID of the HE that receives thecontainer, and the time the transaction occurs. For example, when a toppick (a type of CHE) picks up a container from a tractor, a completeentry for this transaction table should include the ID of the tractor asthe provider of the container, the ID of the container, the ID of thetop pick as the receiver of the container, and the time this pick upoperation occurs. In order to establish such a complete entry, theassociation process needs to go through steps 818 through 830.

Initially in step 818 a search is made to determine if the operation orevent has been reported. When two HEs are involved, due to the delays inthe detectors and the processors on the CHE and the tractor, as well ascommunication delays, the central processor most likely receives anoperation report and an event report at different time instants, andtherefore they are processed one by one in different processing cycles.The association process then searches the transaction table in step 818for candidate operations to determine if the event or operation hasalready been reported. The search can be based on the event type, thetime, and the location of the event.

In one example, a search is made in step 818 to find unmatched containerpickup operations (when the event indicates a pickup operation) occurredwithin a pre-set time window ([t_event−T1, t_event+T2]), where t_eventis the time of the event and T1 and T2 are pre-determined thresholds. Inanother example, the search is made in step 818 to find unmatchedcontainer pickup operations whose locations are within a pre-determineddistance to the location of the reported event. In yet another example,the search is made in step 818 to find unmatched container pickupoperations satisfying both the time window and the location proximityrequirements. If no candidates are found, the association process instep 820 determines that the corresponding operation has not beenreported and the process simply creates a new transaction entry in thetransaction table at step 822 to store the event information. Since thisnewly created transaction entry only contains the ID of the tractor thatprovides the container and the ID of the container, this entry is not acomplete entry and the process marks the entry as “unmatched.”Furthermore, the association process updates its association table instep 822 to remove the association between the container and thetractor.

If candidates are found at step 818, the association process in step 820then identifies a match among the candidates at step 824. In oneembodiment, the association process evaluates each candidate based onfactors including the time gap between the operation and the event, theproximity between the operation location and the event location, thesize of the container, and so on. The association process thencalculates the likelihood of a match for each of the candidates based onthe above factors. For example, if the size of the container in acandidate pickup operation is 40 ft while the size of the container inthe event is 20 ft (a short container), the corresponding likelihoodvalue will be reduced. Also in this embodiment, if the highestlikelihood value is greater than a pre-determined threshold, thecorresponding candidate is determined as a match; otherwise, theassociation process concludes that no match has been found.

A match will be located in step 824 after it is processed previously atstep 822 in previous processing cycles; that is, the matching operationhas been reported earlier. Referring back to the container pickupexample, since the event reporting is considered before the operationreporting, the association process will not be able to find a match forthe reported event in step 824. The process will then be directed tostep 822 via step 826 to create a transaction record for the event andmarks the transaction as “unmatched”. The process then exits and waitsfor the next processing cycle to start at step 802. Assuming, after afew processing cycles, the operation reporting corresponding to theaforementioned event reporting arrives and the association process goesto step 818 through steps 802, 804, and 806. At step 818, the candidateevents will then include the aforementioned event, which will then bedetermined as a match at step 824. Subsequently, the association processwill associate the container with the CHE at step 828; in oneembodiment, this is achieved by adding the container ID to the entrycorresponding to the CHE in the association table. At step 830, theassociation process then further adds to the corresponding transactionentry the ID of the CHE as the HE that receives the container and marksthe transaction as “matched” (or “complete”).

D. Inventory Association Based on Position Sensor and Motion Sensor forDetermining Distance To Last Trustworthy Position

FIGS. 9A and 9B illustrate an example where errors in position estimatescould cause problems for transaction associations. As mentioned earlierin the background herein, inventory association based on positionestimates can suffer from errors in position estimates. However, byincorporating information related to tractors' motion, accuratetransaction association can be achieved based on position estimateswithout equipping tractors with detectors such as vibration detectors orcontainer position detector as described earlier herein. In regards toFIGS. 9A and 9B, assume the position sensor on each HE is a DGPS. It isalso reasonable to assume the DGPS on a CHE is of higher accuracy andtherefore more expensive than the DGPS on a tractor since the number ofCHEs in a container storage facility can be much less than the number oftractors.

FIG. 9A shows a case where a tractor first approaches a top pick duringtime t1 to time t5, arrives at the operation location at time t6, andstops during time t6 through time t10 to receive a container at time t8.The actual location of the tractor at time t1 through time t10 isdenoted by the top view of the tractor with its attached chassis in FIG.9A and the side view in FIG. 9B, while the position measurements fromthe DGPS, P(t), are denoted by “X”. As described in the backgroundherein, the operation location is typically surrounded by containersstacked several tiers high forming makeshift canyons. Such a canyon-likeworking environment causes (long periods of) GPS blockage as well asmultipath that can induce relatively large errors in GPS positions(shown as an “X” not directly associated with the tractor from time t3to t10). Both tractors and CHEs can report their positions (either GPSpositions or GPS-based positions) to a central processor through theironboard communication units, and the central processor then tries toidentify the pair of CHE and tractor that is involved in a transactionbased on the reported positions. Due to the potentially large errors inthe positions (at least in the positions of the tractor), the centralprocessor may fail to make the association. Furthermore, if there isanother tractor in the region, whose GPS positions are actually closerto the GPS position of the top pick due to position errors, the centralprocessor will likely make a wrong association by recognizing this othertractor as the one that received the container.

In FIGS. 9A-9B, GPS-based positioning system is assumed to provideposition estimates; however, as most positioning systems are based onproximity or triangulation, they suffer similar issues and the resultanterrors have similar effects on inventory associations. For example, areal-time locating system (RTLS) is essentially a reverse GPS system andthe canyon-like environment creates blockage and multipath problems forit as well. More specifically, in a RTLS, a mobile positioning unit on aHE transmits radio waves to at least three nearby fixed local receivers,each of which determines the travel time of the radio waves andtransmits the travel time to a central processor. The central processorthen determines the position of the HE based on the radio waves' traveltime to those fixed local receivers. The canyon-like environment betweenstacks of containers can block or reflect the signal the HE tries tocommunicate to the fixed local receivers, resulting in no solutions(i.e., blockage) or erroneous solutions by the central processor.

To ensure correct association of containers and HEs using positionestimates from positioning systems, some embodiments of the presentinvention provide an association determined by incorporating a distancefrom the last trustworthy position (or positions) of the tractor. Thisdistance is referred to as the distance-to-last-trustworthy-position andis calculated based on information related to the motion of the tractor.

FIG. 10 illustrates components of a container tracking system that usesGPS sensors for position determination in an inventory associationsystem. The system of FIG. 10 includes a first mobile unit that caninclude a first positioning unit (GPS sensor) 1002 and an operationdetector 1004 on a CHE 102, a second mobile unit that can include asecond positioning unit (GPS sensor) 1006 and a motion detector 1008 ona tractor 116, a processor 1010 for associating containers with (HEs),and a communication link 1012 between the first and second mobile unitsand the processor to enable information exchange.

The first positioning unit GPS sensors 1002 provides first positions ofthe CHE 102 and the operation detector 1004 provides informationindicating an occurrence of a container operation, such as a pick up ordrop off of a container conducted by the CHE 102. The second positioningunit 1006 provides second positions of the tractor 116 as well asconfidence levels of the positions and a motion detector 1008 providesinformation pertaining to motion of the tractor 116.

The GPS or similar position sensor 1002 and 1006 on each HE provides theposition of the HE. The position sensor 1002 or 1006 can include atleast one of the following: GPS (Global Positioning System) or a DGPS(Differential GPS), INS (Inertial Navigation System), IMU (InertialMeasurement Unit), RTLS (Real Time Locating System), PDS (PositionDetection System), and any other sensors and systems that can be used todetermine the location of HEs.

The motion detector 1008 on the tractor 116 can include at least one ofthe following: a speed sensor that directly measures the speed of thetractor, an accelerometer for measuring the longitudinal acceleration ofthe tractor, which is used to calculate the speed of the tractor, a yawrate sensor, a yaw acceleration sensor, and a compass for providing theheading angle of the tractor 116.

The central processor 1010 detects an occurrence of a containeroperation (including container pick up and drop off) from the operationdetector 1004 as well as relevant position information from the firstposition sensor 1002. The processor 1010 further determines whether thetractor 116 is involved in the container operation based on a pluralityof the following: the location of operation, the motion of the tractor116 before and at the time of occurrence, the operation type, and thesecond positions. If the tractor 116 is determined to be involved in thecontainer operation, the processor 1010 further associates the containerwith the CHE 102 if the operation is a pick up or with the tractor 116if the operation is a drop off.

In one embodiment, the processor 1010 includes multiple local processorsdistributed on each HE 102 and 116 and a central processor provided atthe original location of the main processor 1010. However, as oneskilled in the art can easily recognize, the processor can be providedas an integrated centralized device as shown in FIG. 1O.

To describe how the distance-to-last-trustworthy-position is used in theassociation between containers and HEs, assume the same case shown inFIGS. 9A and 9B and assume the tractor is equipped with a motiondetector such as a speed sensor. As the GPS positions begin todeteriorate when the tractor enters the alley at time t3, thecorresponding confidence level decreases accordingly. Since theconfidence level at time t8 when the container drop off operation occursis low, the processor onboard the tractor retrieves the last trustworthyposition, i.e., the last position that has a high confidence level,which would be P(t2) in this example. Based on the time of the lasttrustworthy position (i.e., t2), the tractor's onboard processor thencomputes the tractor's distance to the last trustworthy position (i.e.,the distance-to-last-trustworthy-position based on the speed collectedfrom time t2 to the time the operation occurs at t8). In this specificcase, since this distance-to-last-trustworthy-position is based on speedonly (i.e., assuming the tractor was travelling straight), it isequivalent to the tractor's travel distance from time t2 through timet8. Since the speed information is almost immune to the canyon-likeworking environment and tractors mostly travel straight in the alleysbetween container stacks, the tractor's calculated travel distanceshould approximate the distance between the operation location and thelast trustworthy position. Therefore, the central processor can identifythe actual tractor that is involved in a container operation andassociate it with the container it receives.

1. Method Steps for Inventory Association Using Position Sensor andMotion Sensor for Determining Distance to Last Trustworthy Position

FIG. 11 is a high-level block diagram showing one embodiment of aprocess for associating containers with HEs in an inventory associationsystem that uses positioning units. Reference can be made to FIG. 9 toillustrate HE positioning during the steps of FIG. 11. Starting at step1102, the processor for a CHE monitors the output of its operationdetector, which can be twistlock sensors, and detects the occurrence ofa container pickup or drop off operation. Upon detection of a containerpickup or drop off operation, the processor for the CHE reports theoperation to a central processor via the onboard communication unit. Thereported information includes the operation type (pickup or drop off),the CHE's location at the time of the operation (including height ifavailable), and the time the operation occurred. The reportedinformation may further include the size of the container as determinedby the length of the spreader bar.

At step 1104, upon receiving a reported container operation from a CHE,the central processor determines whether a tractor is involved. Thedetermination of whether a tractor is involved can be based on a sensorindication such as one indicating height of the container. For instance,if the height corresponds to the height of one or several containers,the CHE is operating on containers on the ground or stacked on top ofother containers. If the height corresponds to the height of a chassis,the operation is with another HE. If the height is not available, thecentral processor always assumes a tractor is involved at step 1104unless no matching tractor can be found (as determined in later steps).

If it is determined that the operation involves no tractor in step 1104,the central processor proceeds to step 1106 to associate the CHE withthe container if the operation is a pickup operation or to disassociatethe CHE with the container if the operation is a drop off operation. Inone embodiment, the central processor maintains an association table tokeep track of the association between containers and HEs, as describedpreviously with respect to steps 810, 814, and 828 in FIG. 8. Also atstep 1106, the central processor updates the inventory tracking databaseto reflect the change of the container location.

If the operation involves a tractor, the central processor proceeds fromstep 1104 to step 1108 to (1) add the operation to a transaction tableand mark the corresponding entry (e.g., as “unmatched”) to indicate thatthe tractor involved is yet to be matched to the operation, and (2)broadcast the operation information, including the type, the location,and the time of the operation as well as the size of the container toall HEs or to HEs nearby by limiting the communication transmit power.Alternatively, the central processor may identify tractors whosepositions are within a pre-determined distance from the operationlocation and communicates the operation information to those tractorsonly. The pre-determined distance should be relatively large to avoidexcluding the correct tractor that may be involved in the operation dueto position errors.

Next at step 1110, upon receiving the operation information from thecentral processor, each tractor determines whether it could be thetractor involved in the operation. In one embodiment, the tractor goesthrough the following steps in making the determination:

Step 1: the tractor examines whether it was at or near zero speed at thetime of the operation based on the speed stored in its storage unit. Ifit was not at or near zero speed, the tractor discards the operationinformation it received without responding to the central processorsince a tractor can only be involved in a container operation when it isfully or almost stopped. If the speed was indeed at or near zero, thetractor then proceeds to step 2.

Step 2: the tractor next examines whether the operation is appropriateby comparing the operation with its own loading status. (This loadingstatus is provided by the central processor whenever the tractor isassociated with a container.) For example, if the tractor already has acontainer on its attached chassis, it cannot receive another 40 ft or 45ft container; hence, if the operation indicates the CHE just set down a40 ft container, then the tractor cannot be the HE involved. If theoperation is in conflict with the tractor's own loading status, thetractor discards the operation information without responding to thecentral processor; otherwise, the tractor proceeds to step 3.

Step 3: the tractor next searches the positions stored in its storageunit for the last trustworthy position (P(t_trustworthy)) based on theconfidence level and retrieves the speed between the time correspondingto the last trustworthy position (t_trustworthy) and the operation time(t_operation). The tractor then calculates thedistance-to-trustworthy-position based on the motion information. Thedistance-to-trustworthy-position (S_motion) can be determined based on aspeed sensor or an accelerometer for proving the speed of the tractor,e.g., as the tractor's travel distance using the speed betweent_trustworthy and t_operation:

S _(motion)=∫_(t) _(—) _(trustworth) ^(t) ^(—) ^(operation)speed×dt

The tractor also calculates the distance between the operation locationand the last trustworthy position:S_distance=P_operation−P(t_trustworthy). The tractor further determinesthe difference between the two distances: S_gap=S_motion−S_distance asthe gap between the tractor and the CHE that performs the operation atthe time of the operation. The tractor then responds to the centralprocessor by communicating the operation information together with itsID and S_gap.

At step 1112, upon receiving responses within a pre-set time periodafter the operation information was first broadcasted (at step 1108),the central processor then evaluates the responses from tractors toidentify the tractor involved in the operation. In one embodiment, theevaluation is simply based on the gap (S_gap) between each tractor andthe CHE, and the tractor that has the smallest gap is chosen as thetractor involved in the operation. The central processor then adds theID of the tractor to the entry of the operation and marks it (e.g., as“matched”) to indicate that all parties involved in the operation areidentified. If the operation is a container pickup operation, thecentral processor further removes the association between the containerand the tractor and associates the container with the CHE; if theoperation is a container drop off operation, the central processorremoves the association between the container and the CHE and associatesit with the tractor. The central communication unit may furthercommunicate the association information back to the tractor for thetractor to keep track of its own loading status.

2. Inventory Association Using Position Sensor and MotionSensor—Determining Distance to Last Trustworthy Position with Motion Notin a Straight Line

In another embodiment, the motion detector on the tractor includes aspeed sensor (or an accelerometer) for providing the speed of thetractor and an angular-motion detector for providing the angular motionof the tractor on the ground. The angular-motion detector can include ayaw rate sensor, a yaw acceleration sensor, and a sensor or device (suchas a compass) for providing the heading angle of the tractor. Thus,instead of assuming the tractor travels straight, the position of thetractor at the time the operation occurred, Pe(t_operation), isdetermined by feeding the last trustworthy position (e.g., P(t2)), thetractor's speed, and the tractor's yaw rate or heading angle into akinematic or dynamic model of the tractor. Subsequently, the tractorcomputes the distance-to-last-trustworthy-position as the distancebetween Pe(t_operation) and the last trustworthy position andcommunicates the distance-to-last-trustworthy-position to the centralprocessor. Alternatively, the tractor can respond to the centralprocessor directly with the calculated position Pe(t_operation) togetherwith the operation information and the ID of the tractor for the centralprocessor to make the final decision of which tractor is the HE involvedin the operation.

The process shown in FIG. 11 has the central processor broadcast orcommunicate the operation reported by a CHE. Alternatively, in anotherembodiment of the system, a CHE directly broadcasts the operationinformation if it determines that a tractor is involved. Thebroadcasting may be set to have limited power to limit the area thebroadcast can cover since only tractors nearby need to receive andprocess the operation information. The tractors can still send responsesto the central processor for it to make the final decision of whichtractor is the one involved in the operation.

FIG. 12 modifies FIG. 9 to illustrate how a tractor heading angle and amap or profile of the container yard can be used to better identify atractor involved with a CHE in a container handling operation. With thetractor equipped with a map showing the profile of the container yard,based on the last trustworthy position and information such as theheading angle of the tractor, the distance-to-last-trustworthy-positionthe tractor can further determine its likely position at the time theoperation occurs. FIG. 12 illustrates the likely positions as aring-shaped area 1202 with its center line as a portion of a circle,whose center is at the last trustworthy position (P(t2)) and whoseradius is the tractor's distance-to-last-trustworthy-position(S_motion). The width of the area depends on the confidence level of thetrustworthy position (P(t2)) and the noise level in the speed signal.The higher the confidence level of the trustworthy position and thesmaller the noise, the narrower the area.

E. Detailed Integrated Association System Using Position, Motion, andEvent Detection

In further embodiments, in addition to the positioning means and themotion detector for providing the motion of the tractor, the tractor canalso be equipped with an event detector for providing informationindicating an occurrence of a container-operation-related eventoccurring to the tractor. The event detector can include a speeddetector 202 and a vibration-detection means 204 as described withrespect to FIG. 2. Alternatively, the event detector may include acontainer-position detector such as radar, LIDAR, and cameras describedwith respect to FIG. 6 that detects the presence of at least onecontainer on the chassis. The processor onboard the tractor then furtherdetects the occurrence of container-operation-related events andincorporates the event detection in the association. In one non-limitingembodiment, at step 110 of FIG. 11, the tractor also examines whether acontainer-operation-related event has been detected within a pre-definedtime window of the time of occurrence for the operation. If so, thetractor responds to the central processor with its ID and S_(gap);otherwise, the tractor does not respond to the central processor.

In addition, the central processor can further incorporate in itsevaluation of responses from tractors factors such as the turn-aroundtime for tractors and sequencing of tractors. For example, the tractorsin a container yard take turns to cooperate with CHEs in containeroperations repeatedly. Therefore, the time gap between recent events fora tractor will be approximately the same. Thus, the central processorcan assess the likelihood of a tractor in an operation by comparing thetime gap between the operation and the previous event of the tractorwith the time gaps between recent events of the tractor. Similarly, ifthe central processor receives responses from multiple tractors, thecentral processor can evaluate the responses with the sequence of thelast events of these tractors. For example, if tractor A had a containerdrop off event before tractor B at the same location and then had acontainer pickup event before tractor B at another same location, it islikely tractor A will have the next container drop off event beforetractor B. The central processor may also monitor the sequence in whichtractors enter an alley based on their (trustworthy) positions andincorporate the sequence in the evaluation of responses. For example, iftractor A enters an alley before tractor B, tractor A is more likely tohave an event occurring in the alley before tractor B since tractorstypically line up to wait for their turn to work with CHEs.

Although the present invention has been described above withparticularity, this was merely to teach one of ordinary skill in the arthow to make and use the invention. Many additional modifications willfall within the scope of the invention, as that scope is defined by thefollowing claims.

1. An event detection apparatus adapted for use with a handlingequipment that can have a chassis attached to it for receiving andtransporting a container, comprising: a vibration detector to measurevibrations of the handling equipment; and a processor to detectcontainer-operation-related events occurring to the handling equipmentbased on the vibrations.
 2. The event detection apparatus of claim 1,wherein the container-operation-related events comprise: pick up of thecontainer from the chassis attached to the handling equipment and dropoff of the container onto the chassis of the handling equipment.
 3. Theevent detection apparatus of claim 1, wherein thecontainer-operation-related events comprise at least one of thefollowing eight types of events: (1) drop off of the container in amiddle of the chassis attached to the handling equipment, (2) drop offof the container at a front of the chassis, (3) drop off of thecontainer at a rear of the chassis, (4) pick up of the container in themiddle of the chassis, (5) pick up of the container at the front of thechassis, (6) pick up of the container at the rear of the chassis, (7)engagement of the chassis with the handling equipment, and (8)disengagement of the chassis from the handling equipment.
 4. The eventdetection apparatus in claim 1, wherein the vibration detector comprisesat least one of the following: a sound detector that detects soundscaused by the impact of a container with the chassis during thecontainer-operation-related event; an accelerometer that detects avertical motion of the handling equipment; a height sensor that detectsa vertical motion of the handling equipment by measuring a height fromthe height sensor to the ground; an angular motion sensor that detects apitch motion of the handling equipment; and an inertial measurement unit(IMU) that comprises at least one of an accelerometer and an angularmotion sensor.
 5. The event detection apparatus in claim 1, wherein theprocessor determines whether a container-operation related event hasoccurred as well as an event type by analyzing the vibrations usingtechniques comprising at least one of pattern recognition, modelmatching, information-based algorithm, cognitive-based algorithm, andrule based logics.
 6. The event detection apparatus in claim 1, whereinthe vibration detector comprises an angular motion sensor that allowsdetermination of a pitch angle of the handling equipment and theprocessor further incorporates a change in the pitch angle of thehandling equipment before and after vibrations occur to detectcontainer-operation-related events.
 7. The event detection apparatus inclaim 1, further comprising a speed detector to provide informationpertaining to whether the handling equipment is at near zero speedincluding zero speed, wherein the speed detector comprises at least oneof the following: a sensor for providing a speed of the handlingequipment, a sensor for providing an acceleration of the handlingequipment, and a sensor for providing a gear position of a transmissionof the handling equipment; and wherein the processor detects thecontainer-operation-related events when the speed detector indicates thehandling equipment is at near zero speed including zero speed.
 8. Theevent detection apparatus in claim 1, further comprising acontainer-presence detector to provide a status indicating a presence ofthe container on the chassis, wherein the processor further incorporatesthe status from the container-presence detector in detectingcontainer-operation-related events and in determining an event type foreach of the container-operation-related events.
 9. An event detectionapparatus adapted for use with a handling equipment that can have achassis attached to it for receiving and transporting a container,comprising: a container-position detector to detect a presence of thecontainer on the chassis attached to the handling equipment and toprovide a status of presence as well as a distance between the containerand the handling equipment; and a processor to receive the status ofpresence and the distance and to detect container-operation-relatedevents occurring to the handling equipment based on changes in thestatus of presence as well as the distances before and after thechanges.
 10. The event detection apparatus of claim 9, wherein thecontainer-operation-related events comprise: pick up of the containerfrom the chassis attached to the handling equipment and drop off of thecontainer onto the chassis of the handling equipment.
 11. An inventoryassociation system for associating containers with handling equipmentfor handling containers in a container storage facility, comprising: anoperation detector, each installed on a unit of first handlingequipment, each first handling equipment unit configured to lift andtransport a container, each operation detector providing informationindicating an occurrence of container operations conducted by arespective unit of the first handling equipment, wherein the containeroperations comprise: a container pickup operation and a container dropoff operation; an event detector, each installed on a unit of secondhandling equipment, each second handling equipment unit having a chassisattached to it for receiving and transporting a container, each eventdetector providing information indicating an occurrence ofcontainer-operation-related events occurring to a respective unit of thesecond handing equipment, wherein the container-operation-related eventscomprise: pick up of a container from the chassis and drop off of acontainer onto the chassis; a processor for associating each containerin each of the container operations with a single unit of the handlingequipment among the first and second handling equipment based on theinformation from the operation detectors and the event detectors; and acommunication link between the operation detectors and the processor aswell as between the event detectors and the processor.
 12. The inventoryassociation system in claim 11, wherein: each of the operation detectorscomprises a plurality of sensor switches for providing a status ofengagement indicating engagement and disengagement of mechanisms thatsecure a container to and release a container from the respective unitof the first handling equipment; and the processor detects an occurrenceof a container operation and a time of occurrence based on changes inthe status of engagement.
 13. The inventory association system in claim11, wherein: each of the operation detectors comprises a vibrationdetector for measuring vibrations of the respective unit of the firsthandling equipment; and the processor detects an occurrence of acontainer operation and time of occurrence based on patterns of saidvibrations. 14 The inventory association system of claim 11, wherein:each of the event detectors comprise a container-position detector thatprovides a status of presence of at least one container on a chassisattached to the respective unit of the second handling equipment as wellas a distance between the container and the respective unit of thesecond handling equipment; and the processor detects an occurrence of acontainer-operation-related event and a time of occurrence based onchanges in the status of presence as well as the distances before andafter the changes.
 15. The inventory association system in claim 11,wherein each of the event detectors comprises a vibration detector toprovide vibration measurements of the respective unit of the secondhandling equipment, and wherein the processor detects an occurrence of acontainer-operation-related event and time of occurrence based on thevibration measurements.
 16. The inventory association system in claim15, wherein: the vibration detector comprises at least one of thefollowing: a sound detector that detects sounds caused by the impact ofa container with the chassis during the container-operation-relatedevent; an accelerometer that detects a vertical motion of the handlingequipment; a height sensor that detects a vertical motion of thehandling equipment by measuring a height from the height sensor to theground; an angular motion sensor that detects a pitch motion of thehandling equipment; and an inertial measurement unit (IMU) thatcomprises at least one of an accelerometer and an angular motion sensor.17. The inventory association system in claim 11, wherein the processorassociates containers with handling equipment by: detecting a given oneof the container operations and a time of occurrence based on theinformation from one of the operation detectors on the first handlingequipment; detecting a given one of the container-operation-relatedevents and a time of occurrence based on the information from one of theevent detector on the second handling equipment; determining whether thegiven container-operation-event matches the given container operation bycomparing the time of occurrence for the given event with the time ofoccurrence for the given operation; and if the givencontainer-operation-event matches the given container operation,associating a container involved in the given container operation withone of the respective units of the first and second handling equipmentbased on at least one of the two types: the type of the given operationand the type of the given event.
 18. The inventory association system inclaim 17, wherein the processor further determines an operation type forthe given container operation and an event type for the givencontainer-operation-related event; and compares the event type for thegiven event with the operation type for the given operation indetermining whether the given container-operation-event matches thegiven container operation.
 19. The inventory association system in claim11, wherein the processor comprises: first distributed processors, eachprovided on one unit of the first handling equipment for detecting acontainer operation and a time of occurrence based on the informationfrom the operation detector on the respective unit of the first handlingequipment, second distributed processors, each provided on one unit ofthe second handling equipment for detecting acontainer-operation-related event and a time of occurrence based on theinformation from the event detector on the respective unit of the secondhandling equipment; and a central processor for associating containerswith individual units of the first and the second handling equipmentbased on the detections from the first and the second distributedprocessors.
 20. The inventory association system in claim 11, wherein:the container-operation-related events include a plurality of typescomprising: (1) drop off of the container in a middle of the chassisattached to the handling equipment, (2) drop off of the container at afront of the chassis, (3) drop off of the container at a rear of thechassis, (4) pick up of the container in the middle of the chassis, (5)pick up of the container at the front of the chassis, (6) pick up of thecontainer at the rear of the chassis, (7) engagement of the chassis withthe handling equipment, and (8) disengagement of the chassis from thehandling equipment; and upon detecting a given one of thecontainer-operation-related events, the processor further determines thetype of the given container-operation-related event based on informationfrom the respective event detector.
 21. The inventory association systemin claim 11, further comprising: a first positioning unit installed oneach unit of the first handling equipment for providing first positionsof the respective unit of the first handing equipment; and a secondpositioning unit installed on each unit of the second handling equipmentfor providing second positions of the respective unit of the secondhanding equipment; wherein the communication link further links thefirst and the second positioning units to the processor and theprocessor incorporates the first and the second positions in theassociation.
 22. An inventory association system for associatingcontainers with handling equipment in a container storage facility,comprising: a first mobile unit, each installed on a unit of firsthandling equipment that can lift and transport a container, comprising:a first positioning unit to provide first positions of a respective unitof the first handing equipment, and an operation detector to provideinformation indicating an occurrence of a container operation conductedby the respective unit of the first handling equipment, wherein thecontainer operation includes at least two types: a container pickupoperation and a container drop off operation; a second mobile unit, eachinstalled on a unit of second handling equipment that has an attachedchassis for receiving and transporting a container, comprising: a secondpositioning unit to provide second positions of a respective unit of thesecond handing equipment; a motion detector to provide informationpertaining to motion of the respective unit of the second handlingequipment in the container storage facility; a processor for associatingcontainers with handling equipments based on the first positions, theinformation from the operation detectors, the second positions, and theinformation from the motion detectors; and a communication link betweenthe first mobile units and the processor as well as between the secondmobile units and the processor configured to transmit information fromthe first and the second mobile units to the processor.
 23. Theinventory association system in claim 22, wherein: each of the operationdetectors comprises a plurality of sensor switches for providing astatus of engagement indicating engagement and disengagement ofmechanisms that secure a container to and release a container from therespective unit of the first handling equipment.
 24. The inventoryassociation system in claim 22, wherein the processor associatescontainers with handling equipments by: detecting a given one of thecontainer operations as well as a respective operation type and a timeof occurrence based on the information from one of the operationdetectors, and determining a location of operation based on the firstpositions of the respective unit of the first handling equipment;determining whether a unit of the second handling equipment is involvedin the given container operation based on a plurality of the following:the location of operation, the operation type, the motion of therespective unit of second handling equipment before and at the time ofoccurrence, and the respective second positions; and if the unit of thesecond handling equipment is determined to be involved in the givencontainer operation, associating a container involved in the givencontainer operation with one of the respective units of the first andsecond handling equipments based on the type of the given containeroperation.
 25. The inventory association system in claim 24, wherein theprocessor, in determining whether the unit of the second handlingequipment is involved in the container operation, further identifies alast trustworthy position among the respective second positionscollected before and at the time of occurrence based on confidencelevels of the respective second positions, calculates adistance-to-last-trustworthy-position based on the motion informationcollected between a time corresponding to the last trustworthy positionand the time of occurrence, and compares thedistance-to-last-trustworthy-position with the distance between the lasttrustworthy position and the location of operation to determine howclose the unit of the second handling equipment was to the location ofoperation at the time of occurrence.
 26. The inventory associationsystem in claim 22, wherein: the processor communicates the detection ofa given one of the container operations as well as a respectiveoperation type and a time of occurrence to the second mobile units; eachof the second mobile units further comprises a processor unit fordetermining a likelihood that the respective second handling equipmentis involved in the given container operation, and each of the secondmobile units communicates the likelihood to the processor; and theprocessor associates containers with handling equipments based on thelikelihood communicated from the second mobile units.
 27. The inventoryassociation system in claim 22, wherein: each of the first mobile unitsfurther comprises a first processor unit configured to detect a givenone of the container operations as well as a respective operation typeand a time of occurrence based on the information from the respectiveoperation detectors, and determine a location of operation based on thefirst positions of the respective unit of the first handling equipment;the first mobile unit communicates the detection of the given containeroperation as well as its operation type and time of occurrence to thesecond mobile units; each of the second mobile units further comprises asecond processor unit configured to determine a likelihood that therespective unit of the second handling equipment is involved in thegiven container operation; and the processor associates containers withhandling equipment based on the likelihood communicated from the secondmobile units.
 28. The inventory association system in claim 22, wherein:each of the second mobile units further comprises an event detector toprovide information indicating an occurrence of a given one ofcontainer-operation-related events occurring to the respective unit ofthe second handing equipment, wherein the container-operation-relatedevent includes at least two types: a container pick up from the chassisand a container drop off onto the chassis; and the processor furtherdetects the given container-operation-related event as well as arespective event type and a time of occurrence for associatingcontainers with handling equipment.
 29. The inventory association systemin claim 22, wherein the processor further incorporates a profile of thecontainer storage facility in associating containers with handlingequipment.
 30. A method for determining a location of a containeroperation with respect to a chassis, comprising: detecting a given oneof container operations and identifying a respective unit of firsthandling equipment that conducts the given container operation, whereinthe first handling equipment can lift and transport a container and thecontainer operations include at least two types: a container pickupoperation and a container drop off operation; determining a unit ofsecond handling equipment that is involved in the container operation,wherein each unit of the second handling equipment has an attachedchassis for transporting the container; and determining the location ofthe container on the chassis based on a status of presence provided by acontainer-presence detector installed on the respective unit of thesecond handling equipment, whereby the location of the given containeroperation with respect to the chassis is determined as the location ofthe container on the chassis.